The subject matter of the present invention relates generally to apparatus for scanning a log to determine its optimum yield axis and positioning the log with its optimum yield axis in alignment with the spindle axis of a veneer lathe. In particular the invention relates to such an apparatus in which the log is scanned by light or other electromagnetic radiation while such log is rotated by the veneer lathe spindles to determine its optimum yield axis and is thereafter positioned by positioning arms to align such optimum yield axis with the lathe spindle axis before peeling sheets of wood veneer from the log with a lathe knife.
Previously it has been proposed in U.S. Pat. No. 3,852,579 granted Dec. 3, 1974 to Sohn et al to determine the optimum yield axis of a log by scanning such log with light beams while the log is rotated in a lathe charger mechanism about spindles which are spaced from the veneer lathe spindles or chucks. Then the lathe charger spindles are moved vertically and horizontally to align the optimum yield axis of the log with a reference axis before transfer to the lathe axis. This has a disadvantage that separate lathe charger spindles and drive motors are required in addition to those used in the veneer lathe. In addition, this scanning during rotation on lathe charger spindles requires a particular type of lathe charger which is not used for many existing lathe apparatus.
In the apparatus of the present invention the log is only rough centered in the lathe charger and then transferred from the lathe charger to the lathe spindles before scanning. Thus, scanning of the log to determine its optimum yield axis is done in the lathe by rotating the log with the lathe spindles. After the optimum yield axis of the log is determined, positioning arms engage the opposite ends of the log and adjust the position of the log to align such optimum yield axis with the lathe spindle axis. Then the lathe spindles reengage the log and such log is rotated while sheets of wood veneer are peeled from the log by the lathe knife. This simplified apparatus results in considerable cost savings.
A log may be scanned by relfecting a light beam from the rotating log to a photoelectric detector to determine the log's optimum yield in the manner of U.S. Pat. No. 3,852,579 of Sohn et al and U.S. Pat. No. 3,992,615 of Bennett et al granted Nov. 16, 1976. Alternatively, it may also be desirable to scan the log by transmitting a light beam past the side of the log to a photodetector positioned on the opposite side of the log from the light source as shown in U.S. Pat. No. 4,197,888 to McGee et al granted Apr. 15, 1980. However, unlike the present invention in all of these prior art patents scanning of the log to determine its optimum yield axis takes place in the lathe charger not on the lathe spindles. In addition, the log is positioned to align its optimum yield axis into a reference position spaced a predetermined distance from the lathe axis, by horizontal and vertical (X-Y) movement of the lathe charger spindles. This requires a complicated and expensive mechanism for adjusting the lathe charger spindles in both vertical and horizontal directions while enabling rotation of such spindles by maintaining them coupled to the drive motors. This problem is avoided in the apparatus of the present invention without X-Y movement of the lathe spindles used for scanning, by employing positioning arms separate from the lathe spindles for adjustment of the log to align its optimum yield axis.
The log scanning and positioning apparatus of the present invention is more versatile than that of the cited patents in that it enables the use of any lathe charger since all scanning and positioning takes place in the lathe, not in the charger. In addition, the present invention enables the scanning and positioning apparatus to be pretested as a unit for accuracy at the manufacturer before installation which is not possible when scanning takes place in the charger.
It has previously been proposed in U.S. Pat. No. 4,246,940 of Edwards et al granted Jan. 27, 1981 to provide a veneer lathe charger apparatus in which the length and position of a transfer arm is adjusted in order to position the log with its optimum yield axis in alignment with the lathe axis after scanning such log in the lathe charger. Thus, this patent is similar to those described above in that it employs lathe charger spindles to rotate the log during scanning to determine the optimum yield axis of such log. However, it differs in that there is no X-Y movement of the charger spindles to adjust the position of the log. Instead, this X-Y movement is produced by pivoting the transfer arm while adjusting the length of such arm.
When light scanning is employed to determine the optimum yield axis of the log, it is preferable to employ a photo detector in the form of a linear array of photo diodes as shown in U.S. Pat. No. 4,221,973 of Nosler granted Sept. 9, 1980. However, other types of photoelectric detectors can also be employed.